Pressure responsive switch



Oct. 21, 1952 HOSFQRD 2,615,104

PRESSURE RESPONSIVE SWITCH Filed Oct. 31, 1949 IN VEN TOR.

Patented Oct. 21, 1952 PRESSURE RESPONSIVE SWITCH Norman F. Hosford, Towaco, N. J., assignor to Bendix Aviation Corporation, Teterboro, N. J., a corporation of Delaware Application October 31, 1949, Serial No. 124,672

11 Claims.

The present invention relates to switches gen erally and more particularly to sealed switches having snap-action make and break characteristics.

In using pressure or temperature responsive devices for actuating control circuits, it is desirable that the switches operated by such devices make and break with a snap-action, and as such circuits usually operate at low voltages the contact surfaces must be kept free from foreign matter. The present invention contemplates the provision of a novel switch which will have a positive make and break and in which the contact surfaces will be protected against dirt.

One object of the present invention, therefore, is to provide a novel, simple switch in which the contact surfaces will be protected against dirt and other foreign matter.

Another object is to provide a novel switch in which the contacts will make and break with a snap-action in response to a slow moving actuating element.

Another object is to provide a novel combination of a condition responsive device and a sealed switch wherein the switch contacts make and break without contact flickering in response to movements of said condition responsive device.

Another object is to provide a novel and simple switch in which the contact elements are maintained in an inert atmosphere and which will operate without contact flickering.

Still another object is to provide a novel, simple and effective switch which will operate without contact flickering by using a permanent magnet as one contact element and a magnetic spring as the other contact element.

The foregoing and other objects and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawing wherein one embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for purpose of illustration and description only, and is not intended as a definition of the limits of the invention.

For a better understanding of the present invention, reference is had to the single figure of the drawing wherein the novel switch assembly hereof, generally designated with the reference character II], is actuated by an aneroid l2 through a contact actuating element or probe l4. The switch illustrated may advantageously be used for a variety of purposes but it is particularly suitable for use with an aneroid responsive to changes in the surrounding ambient pressure and is shown as being enclosed by a bell shaped casing I8 having a switch cavity 20. The casing is provided with an internal shoulder 22 for receiving a cover plate 24 which may be brazed, soldered or swaged to the casing to make an air tight cover therefor. Extending through the cover plate 24 is a pair of contact terminals 26 and 28 insulated from the cover and casing by glass beads 33. Brazed or otherwise securely attached to terminal 28 is a horizontally extending spring contact arm 32 of a magnetic material such as spring steel. Contact terminal 26 has securely attached thereto a permanent magnet 34 which in the illustrated embodiment is shown as .a horse shoe magnet. In order to provide a low resistance path between the contacts, the spring contact arm 32 and magnet 34 are coated with a conductive material such as silver, and in order to provide a smooth contact surface on the spring, a polished conductive plate 36 may be secured thereto.

Aneroid l2 comprises a pair of spaced annular diaphragms 38 and 40 joined along the peripheral edges thereof so that the spacing between the diaphragms is varied in response to changes in the ambient pressure. Diaphragm 38 is provided with a central aperture 42 adapted to be seated on an external shoulder 44 on boss 46 of casing 18 and may be secured thereto as by brazing or soldering. Diaphragm 40 is provided with a rigid centerpiece 48 supporting probe [4 which extends through a central bore 50 in boss 46 to engage contact arm 32 to move it away from or permit it to move against magnet 34. In order to insulate the probe from the contact arm, the probe is tipped with an insulating material indicated at 52.

The cavity within casing l8 and aneroid l2 may be evacuated through a tube 54 and then filled with an inert gas of a pressure sufficient to compensate for the effects of temperature changes on the component parts of the switch assembly, and to reduce arcing between the contact surfaces and the pitting and deterioration thereof. Tube 54 is sealed off by fusion after the proper amount of gas has been introduced into the cavity. Thus the construction described in addition to providing long dependable life for the switch, also provides for temperature compensation to insure uniform operation over a large temperature range. It is well known in the art that due to the extreme temperature range in which aneroids operate, the metal forming the aneroid is subject to undue deflection thereby causing inaccurate pressure indications to result. In order to driver in slot 12 thereof.

- example.

provide for temperature compensation and greater accuracy, the aneroid l2 and casing 18 are filled with an inert gas which varies with the temperature. Therefore, temperature changes will cause an increase or decrease of pressure of the gas within the aneroid l2, resulting in the slight deflection, of the diaphragm walls 38 and 40 to compensate for the efiect of the expansion and contraction of the aneroid H by the temperature change. Probe I4 is threaded to centerpiece 48. When the position of the probe relative to contact arm 32 has been determined, it may be soldered to the centerpiece to prevent gas leakage and to prevent accidental displacement thereof. The downward travel of probe I4 and hence of contact arm 32 is limited by the engagement of shoulder 51 of insert 48 with boss 46.

A light calibrating spring 58 is maintained in compression between centerpiece 48 of diaphragm 4D andadjustable end plate 60. A screw 62 havinga, pointed end 64 seated in a centrally located I recess 86in end plate 60 is in'threaded engagement withmounting plate 68. The compression of spring 58 may be adjusted by loosening stop nut 10 and turning screw 62 by inserting a screw If the unit is carefully designed and if the length of probe [4 is accurately set, the calibration spring 58 may be made very light so as to impose very little loading on aneroid 12' or it maybe dispensed with entirely.

The unit ismounted between a baseplate (not shown) fitting snugly about shoulder 14 of casing [8' and mounting plate 68 for supporting adjusting screw 62.

Coming now to the operation of the switch as- 'sembly described, it will be assumed that it is to be used in aircraft for actuating a control circuit or a warning device when the craft reaches a;predetermined altitude such as 10,000 feet, for At sea level where the atmospheric pressure is at maximum, shoulder of center- 1 piece 48 will be resting against boss 48 and contact arm 32 will be held away from magnet 34.

Asthe craft gainsaltitude, the atmospheric pressure will drop and diaphragm 40 ofaneroid 12 will begin to move away from diaphragm 3S and will carry probe Mwith it against the bias of. spring 58 permitting contact plate 36 on contact spring 32 to move toward magnet'34. If the length of probe 14 and the compression of spring 58 are accurately set, the contactarmBZ will have been permitted to move sufficiently far "into the magnetic field produced by the magnet to permit the attracting force thereof to overcomethe resilient force of the contact arm at 10,000 feet altitude thereby causing the contact to be snapped into engagement with the magnet .to complete the circuit between terminals 26, 28 thereby energizing the associated actuating circuit. Reversely, when the craft descends below the 10,000 feet altitude, the atmospheric pressure will increase thereby compressing the aneroid and forcing probe M'against the spring Although only one embodiment of the invention has been illustrated and described in detail, his to be expressly understood that the invention isnot limited thereto. .made in thezdesign and arrangement of the parts Various changes: can be without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

I claim:

1. In a pressure responsive switch device, the combination comprising a sealed switch chamber, a pair of switch contacts mounted within said chamber, one of said switch contacts comprising a permanent magnet, the other of said contacts comprising a magnetic resilient member normally biased relative to said one contact member, pressure responsive means responsive to changes in the ambient pressure, a member operated by said pressure responsive means and connected to said other contact for opposing said biasing force of said'resilient member whereby said contacts are maintained separated under a certain range of ambient pressure and permitted to move into engagement under another range of ambient pressure, and means for adjusting said member for causing said contacts to engagev at a .desired pressure.

2. In a pressure responsive switchdevice; the combination comprising an aneroid, a switch chamber having a gas therein, said aneroid and said chamber being sealed to the encompassing atmosphere, means communicating said'chambar with the interior of said aneroid and permitting fiow of gas therebetween, a pair of relatively movable switch contacts within said casing, means associated with said aneroid for causin relative movement between said contactsinresponse to changes in ambient pressure. tomake and break engagement between said contacts at a predetermined pressure, and means for adjusting said last named means for causing said contacts to engage at a desired pressure.

3. In a switch assembly, a sealed-casing, an aneroid comprising a pair of separated diaphragms, one of said diaphragms being mounted on said casing, a passage communicating between the interior of said casing and the interior of said aneroid through said one diaphragm, a

probe attached to said other diaphragm and extending through said passage into said casing, a pair of terminals extending from theexterior of said casing to the interior thereof and electrically insulated therefrom, a contact member comprising a permanent magnet connected to one of said terminals, a flexible magnetic contactspring connected at one end thereof to the other of said terminals, the other. end thereof being. arranged for engagement with said contact member and biased towardengaged position, said probe contacting said spring at a point intermediate said ends whereby said contact spring is maintained separated from said contact member at pressures above a predetermined pressure and permitted to move into engagement with said contact memher at said predetermined pressureand means for adjusting the length of said probe.

4. Means for actuatinga switch in accordance with the atmospheric pressures of varyingaltitudes so that the switch closes at a predetermined altitude and opens at an altitude other than the predetermined altitude, comprising a sealed casing, a contact comprising a magnet mounted in said casing, a fioatingcontact of magnetic material within said casing adapted to engage said first-mentioned contact, an aneroid-subject to varying atmospheric pressures, and a member connected to said aneroid for actuating said floating contact, whereby the contactswill be brought adjacent one another to allot/engagement .therebetween throughmagnetic attraction with the atmospheric pressures of varying altitudes so that the switch closes at a predetermined altitude and opens at an altitude other than the predetermined altitude, comprising a switch housing sealed ofi from the atmosphere and containing a fluid, a contact comprising a magnet mounted in said housing, a floating contact of magnetic material within said housing adapted to engage said first mentioned contact, an aneroid sealed to the atmosphere but communicating with said housing to allow free passage of fluid between the interior of said aneroid and said housing, and a member secured to the aneroid slidable partially into the casing, said member cooperating with said floating contact whereby the contacts will be closed at a pressure corresponding to a predetermined altitude and opened at an altitude other than the predetermined altitude.

6. In a pressure responsive switch, a switch housing sealed to the encompassing atmosphere, a pair of switch contacts mounted in said housing, one of said switch contacts being movable to be brought into and out of engagement with the other contact, a pressure responsive member sealed to the atmosphere and movable with changing ambient pressures, a passage connecting the interiors of said housing and said pressure responsive member, and means extending through said passage and movable with said pressure responsive member, said last means being connected for moving said one contact into and out of engagement with said other contact in response to changing ambient pressures.

7. In a switch assembly, a housing sealed to the encompassing atmosphere, a pair of terminals extending from the exterior of said housing to the interior thereof and electrically insulated therefrom, a contact element comprising a magnet connected to one of said terminals, a second contact element of magnetic material connected to said other terminal, pressure responsive means sealed to the encompassing atmosphere and movable in response to changing ambient pressures, a fluid filling said housing and said pressure responsive means for compensatin for the effect of temperature changes on said contact elements and said pressure responsive means, and means movable with said pressure responsive means and engageable with one of said contact elements for causing relative movement between the latter when changing ambient pressures occur.

8. In a switch assembly, a housing sealed to the encompassing atmosphere, a pair of terminals extending through said housing in insulated relation thereto, a contact element includin a magnet connected to one of said terminals and mounted within said housing, a second contact element of magnetic material connected to the other of said terminals and mounted for movement relative to said magnet, pressure responsive means sealed to the encompassing atmosphere and movable in response to changing ambient pressures, means communicatin the interiors of said housing and said pressure responsive memher, a fluid filling said housing and said pressure responsive means for compensating for the eifect of temperature changes on said contact elements and said pressure responsive means, and means movable with said pressure responsive means and engageable with one of said contact elements for causing relative movement between; the latter when changing ambient pressures occur.

9. In a switch assembly, a housing sealedto the encompassing atmosphere, a pair of terminals extending through said housing in insulated relation thereto, a contact element including a magnet connected to one of said terminals and mounted within said housing, a second contact element of magnetic material connected to the other of said terminals and mounted for movement relative to said magnet, a pressure responsive member sealed to the encompassing atmosphere and movable in response to changing ambient pressures, a passage connecting the interiors of said housing and said pressure responsive member, a fluid filling said housing and said pressure responsive member for compensating for the effect of temperature changes on said contact elements and said pressure responsive member, and a member movable with said pressure responsive member and extending through said passage in engagement with said second contact element, said movable member element causing relative movement between said contact elements in response to changes in ambient pressures to make and break engagement between said contacts at predetermined ambient pressures.

10. Means for actuating a switch in accordance with varying ambient pressures so that the switch is closed at a predetermined pressure and opened at a higher or different pressure than the predetermined pressure at which it is closed, comprising a housing sealed from the encompassing atmosphere, a pair of contacts mounted in said housing, one of said contacts including a permanent magnet and the other being of magnetic material, flexible means supporting said other contact to bring the last named contact into and out of engagement with said first mentioned contact, a pressure responsive member having a plurality of resilient walls forming a chamber and sealed to the atmosphere, one of said walls being movable in response to changing ambient pressures, means communicating the interior of said switch housing with said chamber, a fluid filling said housing and said chamber for compensating for the effect of temperature changes on said flexible means and said walls and a member movable with said wall and contacting said flexible means whereby the contacts due to magnetic action open at a pressure higher than that at which they close.

11. Means for actuating a switch in accordance with varying ambient pressures so that the switch is closed at a predetermined pressure and opened at a higher or difierent pressure than the pressure at which it is closed, comprising a sealed housing, a pair of terminals secured to said housing, a contact element comprising a magnet secured to one of said terminals, a flexible member secured to the other terminal, a second contact of magnetic material supported by said flexible member to be brought into and out of engagement with said first mentioned contact element, a pressure responsive member sealed to the atmophere and movable in response to changing ambient pressures, a passage connecting the interiors of said housing and said pressure responsive member, a fluid filling said housing and said pressure responsive member for compensating for the effect of temperature changes on said flexible member and said pressure responsive member, and a member secured to said pressure responsive member and extending through said passage in contact with said '7 8 flexible-member,"whereby the contacts will be 7 brought adjacent one another to allow enga'ge- UNITED STATES PATENTS 'ment therebetween by magnetic attraction at a Number Name Date predetermined pressure and a separation of said 5 0 Martin 4, 930 contacts at a pressure higher than the prede- 5 1 97 0 Twombly t 3, 1934 'terminedpressure- 2,115,518 Clark Apr. 26, 1938 NORMAN HOSFORD- 2,184,241 Newill Dec. 19, 1939 2,315,137 Shaw- Mar. 30, 1943 REFERENCES CITED "The following references are of record in the 10 file of this patent: 

